Expression of the Type IV Collagenase System during Mouse Kidney Development and Tubule Segmentation

Abstract

Abstract. Type IV collagenases matrix metalloproteinase-2 (MMP2) and MMP9 and their related proteins, MT1-MMP, tissue inhibitor of metalloproteinases 1 (TIMP1), TIMP2, and TIMP3, are expressed during kidney morphogenesis and nephrogenesis, but the renal ontogeny of these proteins is only partially known, and their persistence in the adult remains controversial. Their expression was analyzed from early metanephric stages to adulthood by Western blot semiquantitative analysis; laser confocal microscopy of whole-mount kidneys; and a two-step immunoperoxidase labeling procedure using specific markers of proximal tubule (megalin), ascending limb of Henle's loop (Tamm Horsfall protein), and collecting duct (Dolichos biflorusagglutinin lectin). By Western blot, all antigens were detected at day 11.5, peaked at day 16.5, and persisted in the adult at lower levels, although MMP2 was less modulated. All antigens were expressed in metanephric mesenchyme at embryonic day 11.5 and became concentrated in neural cell adhesion molecule-positive—induced mesenchymal cells at day 12.5. Only MT1-MMP and to a lesser extent MMP2 were detected in the ureter bud. At day 16.5, all antigens predominated in the cytoplasm of the proximal tubule, except TIMP1, which was mostly expressed in the ascending limb of Henle's loop and distal tubule. During tubule segmentation, components of the type IV collagenase system showed both spatial and temporal regulation. The distribution of gelatinases was not strictly superimposable to that of their natural inhibitors TIMP, especially for MMP9 and TIMP1. All components persisted in specific segments of the adult renal tubule, where MMP9, MMP2, and MT1-MMP showed an apical expression, suggesting that substrates for these enzymes should be in the tubule lumen or in the apical cell domain and not in the extracellular matrix. These results suggest that a regulated balance of gelatinase activity is required during kidney organogenesis and that gelatinases continue to play a role in adult renal tubule physiology.